He said firearms officers were ready to use “lethal force” on suspected terrorists who posed a deadly risk to the public, whether with guns or knives.

Sir Stephen said: “Officers will make their own decision on the street, using their good judgement – I can’t command them to do something, but if they’re faced with a man with a knife they have a range of options all the way up to lethal.

“We won’t be saying ‘Its not somebody with a Kalashnikov, how dangerous can that be?’

“If somebody is wielding a knife and is doing damage or threatening to do damage, then they will be met with full force.”

Sir Stephen said it would be “foolish” to think another terrorist attack, like the one on Glasgow airport, could not happen, but it was impossible to predict when or where.